That is so bizarre and seems unbelievable. Feels like there is another reason they arent telling you. If you didnt want the stress, why boot the cofounder? If I didnt want the stress I'd try to maintain some ownership and have you step up more.

Something smells fishy, if they don't want the stress why would they want to do all the work alone? And there would still be investors bringing some pressure. They also didn't ask you if you agreed to run the business like a "lifestyle business", they directly ask you to leave. That sounds like a made up excuse.

You probably can't work together anymore now, but you both seem to think the business can be profitable, so if you decide to leave you should be compensated for what you built.

Don't rush the decision. You've worked for 11 months, you can take 2 weeks to talk about it and think things over.